docs: clearly document that ":GH-X" string formatting results in "0X..." (GH-25941)

* clearly document that ":GH-X" string formatting results in "0X..."

* put back the "serial comma"
(cherry picked from commit 92ceb1c8402422412fcbb98ca19448677c667c3c)

Co-authored-by: Tal Einat <532281+taleinat@users.noreply.github.com>